To evaluate the effect of Norplant on lactation and the growth of the infant, a comparative study on lactating women using a cohort approach has been carried out in Klinik Raden Saleh, Department of Obstetrics and Gynaecology, University of Indonesia and Dr Cipto Mangunkusumo General Hospital, Jakarta. The recruitment of the study group took place between 1 November 1983 and 31 August 1984. The inclusion criteria, among others, were age 18-40 years, full term gestation, spontaneous delivery, 4-6 weeks after delivery and plans to breastfeed for at least 6 months. The study group consisted of 60 Norplant acceptors, while the control group consisted of 60 Cu-7IUD acceptors. The subjects had a free choice in deciding which form of fertility regulation they preferred. After 6 months of observation the following conclusions were drawn: Norplant use did not have any effect on maternal body weight, hemoglobin concentration or breastmilk production in comparison with IUD use. The development of infants breastfed by Norplant acceptors was not delayed compared to that of infants breastfed by IUD acceptors.